Selective etch rate monitor

ABSTRACT

Embodiments include a real time etch rate sensor and methods of for using a real time etch rate sensor. In an embodiment, the real time etch rate sensor includes a resonant system and a conductive housing. The resonant system may include a resonating body, a first electrode formed over a first surface of the resonating body, a second electrode formed over a second surface of the resonating body, and a sacrificial layer formed over the first electrode. In an embodiment, at least a portion of the first electrode is not covered by the sacrificial layer. In an embodiment, the conductive housing may secure the resonant system. Additionally, the conductive housing contacts the first electrode, and at least a portion of an interior edge of the conductive housing may be spaced away from the sacrificial layer.

BACKGROUND 1) Field

Embodiments relate to the field of etching processes for semiconductormanufacturing and, in particular, to systems and methods for providingreal time etch rate monitoring in radical only etching processes.

2) Description of Related Art

In semiconductor etching processes, it is often difficult to monitor theetch rate in real time. As such, etch rates can typically only bedetermined by calculating the difference between a starting thickness ofa film and an ending thickness of the film and dividing the differenceby the total processing time. However, it is to be appreciated thatmonitoring the etch rate in real time provides additional informationthat may be used to tune etching processes so that they are precise andhave a higher degree of repeatability, among other advantages.

Some solutions to provide real time etch rate monitoring have beendeveloped. For example, optical emission spectroscopy (OES) andabsorption spectroscopy are solutions that have been used in traditionalplasma etching chambers. In OES, the intensity of the optical emissionfrom the plasma may be correlated to the etch rate. In absorptionspectroscopy a line of sight path through the process volume is needed.However, a line of sight through the process volume is often notavailable in high volume manufacturing equipment.

SUMMARY

Embodiments include a real time etch rate sensor and methods of forusing a real time etch rate sensor. In an embodiment, the real time etchrate sensor includes a resonant system and a conductive housing. Theresonant system may include a resonating body, a first electrode formedover a first surface of the resonating body, a second electrode formedover a second surface of the resonating body, and a sacrificial layerformed over the first electrode. In an embodiment, at least a portion ofthe first electrode is not covered by the sacrificial layer. In anembodiment, the conductive housing may secure the resonant system.Additionally, the conductive housing contacts the first electrode, andat least a portion of an interior edge of the conductive housing may bespaced away from the sacrificial layer.

Additional embodiments may include a radical only etching process tool.In an embodiment, the radical only etching process tool may include aremote plasma chamber and a main processing chamber coupled to theremote plasma chamber. In an embodiment, the main processing chamberinclude an upper portion and a lower portion that is separated from theupper portion by an ion filter, and a pump liner formed around apedestal in the lower portion. In an embodiment, the radical onlyetching process tool may also include a real time etch rate sensorlocated in the lower portion of the main processing chamber. In anembodiment, the real time etch rate sensor includes a resonant systemand a conductive housing. The resonant system may include a resonatingbody, a first electrode formed over a first surface of the resonatingbody, a second electrode formed over a second surface of the resonatingbody, and a sacrificial layer formed over the first electrode. In anembodiment, at least a portion of the first electrode is not covered bythe sacrificial layer. In an embodiment, the conductive housing maysecure the resonant system. Additionally, the conductive housingcontacts the first electrode, and at least a portion of an interior edgeof the conductive housing may be spaced away from the sacrificial layer.

Additional embodiments may include methods for etching a substrate witha closed loop process recipe. In an embodiment, the method may includeexecuting the process recipe on a substrate in a processing chamber. Theprocess recipe may include one or more process parameters and anendpoint criterion that is determinable from outputs obtained from areal time etch rate sensor located in the processing chamber. The methodmay then continue by determining whether the endpoint criterion issatisfied by analyzing one or more outputs from the real time etch ratesensor. Embodiments may then include terminating the process recipe oncethe endpoint criterion is satisfied. In some embodiments, the endpointcriterion is a total thickness of material removed, and the one or moreoutputs from the real time etch rate sensor that are used to determineif the endpoint criterion is satisfied may be a resonance frequency ofthe real time etch rate sensor prior to executing the process recipe anda present resonance frequency of the real time etch rate sensor afterthe process recipe has been initiated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a processing tool for implementinga radical only etching processing, according to an embodiment.

FIG. 2A is a cross-sectional illustration of a sensor that may be usedto provide real time etch rate monitoring, according to an embodiment.

FIG. 2B is plan view illustration of the sensor in FIG. 2A, according toan embodiment.

FIG. 2C is plan view illustration of a sensor that may be used toprovide real time etch rate monitoring for more than one material,according to an additional embodiment.

FIG. 2D is plan view illustration of a sensor that may be used toprovide real time etch rate monitoring for more than one material,according to an additional embodiment.

FIG. 3A is a schematic illustration of a processing tool forimplementing a radical only etching process that shows the location of asensor, according to an embodiment.

FIG. 3B is a schematic illustration of a processing tool forimplementing a radical only etching process that shows a sensorintegrated into a pump liner, according to an additional embodiment.

FIG. 4 is a process flow diagram that describes a process for using asensor for closed loop process control, according to an embodiment.

FIG. 5 is a process flow diagram that describes a process for using asensor for substrate to substrate feed forward process control,according to an embodiment.

FIG. 6 illustrates a block diagram of an exemplary computer system thatmay be used in conjunction with processes that include monitoring theetch rate of a radical only etching process in real time, in accordancewith an embodiment.

DETAILED DESCRIPTION

Systems and methods for using a sensor for real time etch ratemonitoring in a radical only etching process are described in accordancewith various embodiments. In the following description, numerousspecific details are set forth in order to provide a thoroughunderstanding of embodiments. It will be apparent to one skilled in theart that embodiments may be practiced without these specific details. Inother instances, well-known aspects are not described in detail in orderto not unnecessarily obscure embodiments. Furthermore, it is to beunderstood that the various embodiments shown in the accompanyingdrawings are illustrative representations and are not necessarily drawnto scale.

As noted above, real time etch rate monitoring provides information thatmay be used to improve various process outcomes of the etching process.While OES and absorption spectroscopy have been used in plasma etchingoperations, they are significantly limited in radical only etchingprocesses. For example, in a radical only etching process OES is notfeasible, because there is not a significant optical emission from theradical species in the process volume where the substrate is etched. Inabsorption spectroscopy, in addition to line of sight requirementsdescribed above, the absorption of light by many radical species usedfor etching is strongest in the deep ultra violet (UV) frequencies.Accordingly, the optics needed for measurements are complex andexpensive. Furthermore, the signal to noise ratio in absorptionspectroscopy is poor because there are relatively few radicals comparedto background parent molecules.

As used herein, a radical only etching process is an etching processthat relies substantially on radical species to remove a material. FIG.1 is a schematic cross-sectional illustration of a processing tool 100that may be used to implement a radical only etching process, accordingto an embodiment. In an embodiment, the processing tool 100 may includea remote plasma. One or more processing gasses may be flown into aremote plasma chamber 110 through valves (not shown). The processinggasses may be ionized with a power source (e.g., a radio-frequencysource) to form a plasma that includes ions 124 and radicals 126. Plasmamay then be transported through a remote plasma transport region 112 tothe main processing chamber 116. In an embodiment, the main processingchamber 116 may include an upper region 117 and a lower region 118. Theupper region 117 and the lower region 118 may be separated by an ionfilter 122. In an additional embodiment, the ion filter 122 may also belocated in the transport region 112 or another intermediate chamberbetween the remote plasma chamber 110 and the main processing chamber116.

According to an embodiment, the ion filter 122 may prevent ions 124 frompassing to the lower region 118 of the main processing chamber 116,while at the same time allowing the radical species 126 to pass throughto the lower region 118 of the main processing chamber 116. For example,in the upper region 117 the ratio of radical species 126 to ions 124 maybe approximately 1:1, and in the lower region 118 the ratio of radicalspecies 126 to ions 124 may be approximately 25,000:1 or greater. Insome embodiments, the ratio of radical species 126 to ions 124 may beapproximately 100,000:1 or greater. Due to the high ratio of radicals126 to ions 124, etching processes using such a processing tool 100 maybe considered a radical only etching process. The radical species 126may then interact with a surface of a substrate 105 positioned on apedestal 106. In an embodiment, a pump liner 108 may be formed aroundthe perimeter of the pedestal 106 in order to direct the flow ofradicals 126 towards the substrate 105. It is to be appreciated thatradical only etching process tool 100 illustrated in FIG. 1 is exemplaryin nature and highly simplified by removing components known to thoseskilled in the art (e.g., vacuum pumps, heating elements, electricalcomponents, among others) in order to not obscure aspects of variousembodiments. In a particular embodiment, the radical only etchingprocess tool 100 may be a Producer® Selectra™ Etch system manufacturedby Applied Materials, Inc. of Santa Clara, Calif.

Since OES and absorption spectroscopy are not viable solutions for realtime etch rate monitoring in such radical only etching processes,embodiments described herein include a sensor that uses a resonantsystem for etch rate monitoring. A resonant system measures a change inthe resonance frequency of a resonating body. As the mass of theresonant system changes, the resonance frequency of the resonating bodychanges monotonically. When such a sensor is used to monitor the etchrate in a radical only etching process, the resonant system may includea sacrificial film that is formed over one face of the resonating bodyand is exposed to the radicals in the processing tool 100. The radicalsetch away the sacrificial film, and the overall mass of the resonantsystem decreases. The decrease in mass of the resonant system causes anincrease in the resonance frequency of the resonating body, which ismeasured in real time, and the rate of change of resonance frequency isconverted to a rate of change of mass of the resonant system. The rateof change of mass of the resonant system may then be converted to a rateof change of thickness since the density of the film material is known.

Sensors that use resonant systems have been used in the past to providereal time deposition rates for deposition processes (e.g., evaporation,sputtering, and the like). However, previous etching solutions were notable to utilize sensors that use resonant systems for various reasons.One reason is that previous etching processes (e.g., reactive ionetching (RIE)) are not purely a material removal process. For example,as a material is being removed, additional byproducts may redeposit ontothe substrate. For example, in a silicon etch with RIE a polymer may beredeposited onto the surfaces. This polymer improves anisotropicetching, but also adds to the mass of the substrate. Accordingly, if asensor with a resonant system were used in such an etching process, thetotal mass of the film removed could not be accurately determinedbecause there would also be an increase in mass that is attributed tothe polymer redeposition. Additionally, the presence of the ions in theplasma and the RF power produce significant interference with the signalfrom the sensor. As such, a reliable reading with a suitable signal tonoise ratio is much more difficult to obtain compared to the processenvironment in a radical only etching process.

Referring now to FIG. 2A, a cross-sectional illustration of a sensor 250that may be used to provide real time etch rate monitoring during aradical only etching process is shown, according to an embodiment. In anembodiment, the sensor 250 may include a resonant system 261 and ahousing 266. Embodiments may include a resonant system 261 that includesa resonating body 262, a first electrode 264, a second electrode 265,and a sacrificial layer 270.

The resonating body 262 may be a material that changes resonantfrequency as the mass of the resonant system 261 changes. In anembodiment, the resonating body 262 may be a piezoelectric material. Forexample, the resonating body 262 may be quartz, sapphire, semiconductingmaterials, such as silicon, germanium, or other III-V semiconductormaterials, lead zirconate titanate (PZT), or the like.

In an embodiment, the resonant system 261 may include a first electrode264 formed on a first surface of the resonating body 262 and a secondelectrode 265 formed on a second surface of the resonating body 262 thatis opposite from the first surface. The first electrode 264 and thesecond electrode 265 may be any suitable conductive material. In oneembodiment, the first and second electrodes 264, 265 may be aluminum, orthe like. In the illustrated embodiment, the first and second electrodes264, 265 do not cover the entire surface of the resonating body 262, butit is to be appreciated that embodiments are not limited to suchconfigurations. For example, the first and second electrodes 264, 265may cover the entire surface of the resonating body 262 in someembodiments. Additionally, embodiments may include first and secondelectrodes 264, 265 that have different surface areas. For example, thesecond electrode 265 may have a smaller surface area than the firstelectrode 264. In yet another embodiment, the surface areas of the firstand second electrodes 264, 265 may be substantially the same.

In an embodiment, the resonant system 261 may include a sacrificiallayer 270 formed on a surface of the first electrode 264. The additionof the sacrificial layer 270 changes the mass of the resonant system 261and, therefore, alters the resonance frequency of the resonating body262. Accordingly, as the thickness of the sacrificial layer 270 isreduced during an etching process, the resonance frequency of theresonating body 262 changes monotonically, as described above. In anembodiment, the sacrificial film 270 is the same material that is to beetched with a radical only etching process. For example, the sacrificialfilm 270 may be a dielectric material, a semiconductor material, or ametallic material.

The sacrificial layer 270 may be formed with a known thickness T. In anembodiment, the thickness T of the sacrificial layer 270 may be greaterthan the thickness of the material that will subsequently be etched awayfrom a substrate being processed. Since etching is a subtractiveprocess, increasing the thickness T of the sacrificial layer 270increases the lifespan of the sensor 250 before the sensor 250 needs tobe replaced or refurbished. For example, the thickness T of thesacrificial layer 270 may be sufficient to run a given etching processrecipe multiple times without needing to replace the sensor 250. In anembodiment, the thickness T of the sacrificial layer 270 may be chosento allow for a process recipe to be run ten or more times before thesacrificial layer 270 is completely removed. Additional embodiments mayallow for a process recipe to be run one hundred or more times beforethe sacrificial layer 270 is completely removed. Additional embodimentsmay allow for a process recipe to be run one thousand or more timesbefore the sacrificial layer 270 is completely removed. In someembodiments, the sacrificial layer may have a thickness T that allowsfor a process recipe to be run ten thousand times before the sacrificiallayer 270 is completely removed.

In an embodiment, the sacrificial layer 270 is formed over a portion ofthe first electrode 264 such that at least a portion of the firstelectrode 264 remains exposed. At least a portion of the first electrodeis exposed in order to provide a location where an electrical contact tothe first electrode 264 may be made. For example, the sacrificial layer270 may be formed in the center of the first electrode 264, leaving anexposed portion of the first electrode 264 around the periphery of thesacrificial layer 270.

In an embodiment, the resonant system 261 may be secured by a housing266. In an embodiment, the housing 266 may be a conductive material. Inan embodiment, the housing 266 may provide an electrical connectionbetween a frequency bridge 267 and the first electrode 264. In anembodiment, the second electrode 265 may be electrically coupled to thefrequency bridge 267. In some embodiments, the housing 266 may begrounded so that the first electrode 264 is held at ground potential.

Referring now to FIG. 2B, a top view of the sensor 250 is shown,according to an embodiment. In an embodiment, an interior edge 268 ofthe housing 266 is spaced away from the sacrificial layer 270 by a gapG. The gap G exposes a portion of the first electrode 264. In anembodiment, the gap G may be approximately 5 mm or less. In anembodiment, the gap G may be approximately 5% of the radius of the firstelectrode 264 or less. In the illustrated embodiment, the gap G betweenthe interior edge 268 of the housing 266 and the perimeter of thesacrificial layer is substantially uniform since the sacrificial layer270 is the same shape as the opening in the housing 266 and issubstantially centered within the opening of the housing 266. However,embodiments are not limited to such configurations and the gap G may notbe substantially the same at all points between the interior edge 268 ofthe housing and the perimeter of the sacrificial layer 270. For example,the sacrificial layer 270 may be a different shape than the opening inthe housing 266 and/or the sacrificial layer 270 may not besubstantially centered within the opening in the housing 266. Inembodiments, the connection between the housing 266 and the firstelectrode 264 is not continuous along the interior edge 268; however, insuch embodiments, the gap G is still present for one or more of thediscrete connection locations between the housing 266 and the firstelectrode 264.

Since the first electrode 264 is exposed to the radicals in the radicalonly etching process, embodiments include a first electrode 264 that isformed with a material that is substantially resistant to the radicalonly etching process used to etch the sacrificial layer 270. Otherwise,the first electrode 264 may be etched along with the sacrificial layer270, and several problems would arise. One such problem would be thatthe change in mass of the resonant system 261 would be the sum of thematerial loss of the first electrode 264 and the material loss of thesacrificial layer 270. As such, the change in resonance frequency of theresonating body 262 would not correspond to the etch rate of thesacrificial layer 270 only. Additionally, removal of the first electrode264 and/or the housing 266 by the radical only etching process reducesthe useable service life of the sensor 250.

In the illustrated embodiment, the sensor 250 is shown having resonantsystem 261 that includes a single sacrificial layer 270. However,embodiments are not limited to such configurations. For example,multiple sacrificial layers 270 ₁-270 _(n) may be formed over the firstelectrode 264. In such embodiments, so long as each of the sacrificiallayers have a high etch selectively with respect to each other, a singlesensor 250 may be used to provide real time etch rates for severaldifferent etching recipes. For example, a first etch of a silicon oxidelayer may be monitored and then a second etch of a silicon layer may bemonitored without needing to change the QCM 250. Some exemplaryembodiments that include multiple sacrificial layers 270 ₁-270 _(n) areshown in the plan view illustrations in FIGS. 2C and 2D.

In the embodiment illustrated in FIG. 2C, a plurality of sacrificiallayers 270 ₂-270 _(n) are formed in concentric rings around a firstsacrificial layer 270 ₁. In an embodiment, each sacrificial layer 270₁-270 _(n) may be substantially the same thickness. In an additionalembodiment, two or more of the sacrificial layers 270 ₁-270 _(n) mayhave different thicknesses. Providing sacrificial layers with differentthicknesses may allow for a longer service life before the sensor 250needs to be refurbished. For example, the processing used in thefabrication of a semiconductor device may include removing a greaterthickness of a first material that corresponds to the first sacrificiallayer 270 ₁ than a thickness of a second material that corresponds tothe second sacrificial layer 270 ₂. As such, a sensor 250 with a firstsacrificial layer 270 ₁ that has a thickness that is greater than athickness of the second sacrificial layer 270 ₂ may ensure that bothsacrificial layers are completely consumed after approximately the samenumber of substrates have been processed.

Additional embodiments include a plurality of sacrificial layers 270₁-270 _(n) that are formed in patterns over the surface of the firstelectrode 264 other than concentric rings. For example, in FIG. 2D eachsacrificial layer 270 ₁-270 _(n) is formed in a different region. Insome embodiments, each of the sacrificial layers 270 ₁-270 _(n) may bespaced apart from each other. In other embodiments, each of thesacrificial layers 270 ₁-270 _(n) may contact one or more othersacrificial layers. Furthermore, while each sacrificial layer 270 ₁-270_(n) is shown as having substantially the same area, embodiments are notlimited to such configurations and the area of each sacrificial layer270 ₁-270 _(n) may be different from each other. Similar to theembodiment described with respect to FIG. 2C, the thickness of eachsacrificial layer 270 ₁-270 _(n) may be substantially similar to eachother, or the thickness of each sacrificial layer 270 ₁-270 _(n) may bedifferent.

Referring now to FIG. 3A, a schematic illustration of a processing tool300 that includes a sensor 250 is shown, according to an embodiment. Inan embodiment, the sensor 250 may be electrically coupled to a monitor383 that is located outside the processing tool 300 by a probe 382. Themonitor 383 may include circuitry for monitoring the resonance (e.g., afrequency bridge) and any other electrical components and/or circuitryneeded for monitoring the etch rate in real time. Additional embodimentsmay include a monitor 383 that is communicatively coupled with acomputer system (not shown) that is used to control the etching processin the processing tool 300. In an embodiment, the probe 382 may beinserted through a port 384 in the processing tool 300. For example, theprobe 382 may be inserted into the lower region 318 of the processingtool 300 proximate to the pedestal 306. Locating the sensor 250 in thelower region 318 results in the sensor 250 being exposed to the radicalswithout substantial interaction with ions formed in the remote plasma.In an embodiment, the sensor 250 may be oriented so that the face of thefirst electrode is substantially parallel to a face of pedestal 306 onwhich a substrate (not shown) may be placed during processing. Thoughnot shown in FIG. 3A, embodiments may include a sensor 250 that islocated between a pump liner and the pedestal 306 or outside of the pumpliner. In an embodiment, the sensor 250 may be located at a position inthe processing tool 300 that allows for the etch rate of the sacrificiallayer 270 to be representative and correlatable to the etch rate of amaterial formed on a substrate positioned on the pedestal.

In an additional embodiment illustrated in FIG. 3B, the sensor 250 maybe integrated into a pump liner 308 in the lower region 318 of theprocessing tool 300. As illustrated, the probe 382 may extend through anopening in the pump liner 308 with the sensor 250 being seated in theopening. For example, the face of the first electrode may be orientedtowards the pedestal 306 and be substantially perpendicular to a surfaceof the pedestal 306 on which the substrate may be placed duringprocessing. Integrating the sensor 250 with the pump liner 308 allowsfor the flow of radicals that passes by the sensor 250 to besubstantially similar to the flow of radicals that passes by a substrate(not shown) that is processed in processing tool 300. In an embodiment,the sensor 250 may be located at a position in the processing tool 300that allows for the etch rate of the sacrificial layer 270 to berepresentative and correlatable to the etch rate of a material formed ona substrate positioned on the pedestal. In an additional embodiment, thesensor 250 may be displaced within the processing tool 300 by extendingor retracting the probe 382. As illustrated by the arrow in FIG. 3B, theprobe 382 may be retracted so that the sensor 250 passes through a gatevalve 385 and is removed from the lower region 318 of the processingtool 300. For example, the valve 385 may separate the lower region 318of the processing tool 300 from an antechamber 386. In an embodiment,the antechamber 386 may be a storage chamber for the sensor 250 that isisolated from the radicals in the lower region 318. Accordingly, whenthe sensor 250 is positioned in the antechamber 386, the sensor will notbe exposed to the etching process used to remove the sacrificial layer.In an embodiment, the antechamber 286 may include a vacuum pump and gaslines for purging the antechamber 286. This configuration providesseveral additional advantages that may increase the useable service lifeof the sensor 250 and/or decreases the downtime of the processing tool300 when the sensor 250 is replaced after the useable service life ofthe sensor 250 is exceeded.

For example, in some embodiments it may not be necessary to provide realtime etch rate monitoring for every substrate that is processed in theprocessing tool 300 (e.g., the real time etch rate may only be monitoredfor a single substrate in each lot of substrates, the real time etchrate may be monitored for every second, third, fourth, fifth, etc.,substrate, or any other desired sampling plan). As such, embodimentsinclude retracting the sensor 250 into the antechamber 386 wheneveractive etch rate monitoring is not needed in order to extend the useableservice life of the sensor 250. Since the antechamber 386 is able to bepurged and pumped down to the processing pressure (i.e., the antechamber386 may function similar to a load lock), the main processing chamberdoes not need to be depressurized between uses of the sensor 250.Furthermore, during an in situ chamber cleaning operation, the sensor250 may be protected by being retracted into the antechamber 386. Assuch, a processing operation that may otherwise substantially reduce theuseable service life of the sensor 250 due to an aggressive etchingchemistry may be implemented without damaging the sensor 250.

In embodiments that include an antechamber 386 and gate valve 385, thesensor 250 may also be replaced without needing to depressurize and/oropen the main processing chamber. Instead, the antechamber 386 may bedepressurized and opened to retrieve the used sensor 250 and insert areplacement sensor 250. Since the antechamber 386 is smaller than themain processing chamber, the time needed to pump the antechamber 386back down to the processing pressure is reduced. Furthermore, the mainprocessing chamber does not need to be opened, and there is no need toseason the main processing chamber after the sensor 250 is replaced.

As noted above, the ability to monitor etch rates in real time providesseveral advantages that improve various processing outcomes used duringthe processing of a single substrate or a plurality of substrates. Forexample, in some embodiments real time etch rate monitoring may allowfor closed loop process control that allows for an etching processrecipe to be dependent on the actual thickness of material removed. Inanother embodiment, chamber matching between multiple processing toolsexecuting a single processing recipe may be implemented when real timeetch rate monitoring is enabled. Additional embodiments may allow forrefining an etching process recipe as multiple substrates are processedby using substrate to substrate feedforward control. Further embodimentsmay allow for chamber health monitoring that allows for more accuratedetermination of when process tool maintenance is needed.

In a particular embodiment, a sensor 250 substantially similar to thosedescribed above may be used to enable etching process recipes that areimplemented with closed loop process control. Previously, when real timeetch rate monitoring is not able to be implemented, the process reciperelies on a preset processing duration. Relying on a preset duration maybe a problem because the conditions in the processing chamber may varybetween substrates (e.g., due to variations in chamber conditions,inconsistent flow of radicals into the lower region, inconsistencies inprevious processing operations on the substrates, etc.). However,embodiments that include a sensor 250, such as those described herein,provide the ability to implement closed loop process control that is nottime dependent. Instead, the endpoint of the processing recipe may bedetermined by the actual thickness of material that is removed. Forexample, if the processing recipe is designed to remove 30 nm ofmaterial thickness, then the processing recipe may be terminated oncethe sensor 250 produces outputs that indicate 30 nm of materialthickness has been removed from the substrate instead of approximatingthe removal of material from the substrate based on time. An exemplaryprocess recipe that uses closed loop process control is shown in processflow chart 490 illustrated in FIG. 4.

Starting with the processing operation 491, embodiments may includeexecuting a radical only etching process recipe. In an embodiment, theprocessing recipe may include any number of processing parameters thatare to be used in the etching process. For example, the processingrecipe may include process parameters, such as the desired substratetemperature, the flow rate of one or more processing gasses, thepressure in the processing chamber, or the like. Additionally, theprocessing recipe may include one or more endpoint criteria. In aparticular embodiment, one endpoint criterion may be a parameter that isdeterminable from outputs obtained from the sensor 250. For example, theendpoint criterion may be a total thickness of material removed from thesubstrate, which may be determined by the change in resonance frequencyof the resonating body 262, as is described above.

Referring now to processing operation 492, embodiments may continue byanalyzing the outputs obtained from the sensor 250 to determine if theone or more endpoint criteria are satisfied. For example, the sensor 250may determine if the desired thickness of material has been removed fromthe substrate by comparing an initial resonance frequency of theresonating body 262 (prior to the initiation of the processing recipe)to the present resonance frequency of the resonating body 262. When thedesired endpoint criterion is not satisfied, the process 490 may loopback to processing operation 491 and the processing recipe continues tobe executed. In an embodiment, processing operation 492 may beimplemented substantially continuously or at predetermined intervals(e.g., every 5 second or less, every 1 second or less, every 0.01 secondor less, or any other desired interval). According to an embodiment,once the desired endpoint criteria has been satisfied, the process maycontinue to processing operation 493 and the processing recipe may beterminated.

In an additional embodiment, the sensor 250 may be utilized to providechamber matching. Chamber matching allows for multiple processing toolsto process a plurality of substrates in parallel. In properly matchedchambers, the process outcome of each substrate is substantially thesame even when they are processed in different chambers. Accordingly,the differences between different lots or batches of substrates may beminimized and process uniformity is improved. For example, when eachprocessing tool utilizes a sensor 250 to implement a closed loopprocessing recipe similar to the processing described above with respectto FIG. 4, the thickness of material removed from every substrate,regardless of which processing tool is used, will be substantially thesame. As such, even when the processing tools have different etch ratesdue to variances in processing conditions, the process outcome may stillbe highly uniform.

According to an additional embodiment, real time etch rate monitoringwith a sensor 250 may also allow for substrate to substrate feedforwardcontrol of a processing recipe. Such an embodiment may be particularlybeneficial because real time etch rate monitoring allows for theprocessing recipe to be modified after each substrate is processed.Therefore, even as processing conditions within the processing toolchange (e.g., due to chamber cleanliness, or the like), a uniformprocess outcome may still be obtained. An example of a process for usingsubstrate to substrate feedforward control of a processing recipe isillustrated in process flow 590 in FIG. 5.

In an embodiment, the process may begin with processing operation 591 byexecuting a processing recipe on a first substrate in a processingchamber. In an embodiment, the processing recipe is a recipe for aradical only etching process. In an embodiment, the processing recipemay include any number of processing parameters that are to be used inthe etching process. For example, the processing recipe may includeprocessing parameters, such as the desired substrate temperature, theflow rate of one or more processing gasses, the pressure in theprocessing chamber, or the like. In an embodiment, the process recipemay include one or more endpoint criteria. In a particular embodiment,one endpoint criterion may be a parameter that is determinable fromoutputs obtained from the sensor 250. For example, the endpointcriterion may be a total thickness of material removed, which may bedetermined by the change in resonance frequency of the resonating body262, as is described above.

In an embodiment, the process flow advances to processing operation 592where the outputs of the sensor 250 are analyzed to determine whetherthe endpoint criterion has been satisfied. If the endpoint criterion hasnot been satisfied, the process may loop back to operation 591, asshown. When the endpoint criterion has been satisfied, the procedure mayadvance to processing operation 593 and the process recipe isterminated. Thereafter, the procedure may advance to processingoperation 594 where data from the processing of the first substrate isfed forward and used to modify the processing recipe for use on a secondsubstrate. In an embodiment, the processing recipe may be modified bychanging one or more of the processing parameters of the process recipe.For example, if the endpoint criterion took longer than expected toreach during the execution of the process recipe, then one or more ofthe processing parameters of the processing recipe may be modified todecrease the time needed to reach the endpoint criteria (e.g., byincreasing the substrate temperature, increasing the flow rate of theprocessing gasses, etc.). Therefore, embodiments may include using feedforward information from a processing recipe executed on a firstsubstrate in order to modify the process recipe for use on a secondsubstrate. As such, the process recipe may be refined to allow for adesired outcome to be obtained in a more efficient manner.

Furthermore, process flow 590 may be extended to allow for processchamber health monitoring. Particularly, embodiments may include theadditional operation of comparing the modified process recipe with theoriginal process recipe to determine if there is a significant enoughvariance such that chamber maintenance is needed, as illustrated inprocessing operation 595. For example, comparing the modified processrecipe with the original process recipe may include calculating thedifferences between one or more of the processing parameters in themodified process recipe and the original process recipe. In anembodiment, the chamber maintenance may include any adjustment to thechamber conditions, such as a chamber clean or replacement and/orrefurbishment of one or more components that have been determined to beat the end of their service life.

In an embodiment, a significant variation that indicates that a chamberclean is needed may be when the difference of one or more of the processparameters in the modified process recipe and the original processrecipe exceeds a predetermined threshold value. In an embodiment, thepredetermined threshold value may be a maximum percentage change in agiven process parameter. For example, the predetermined threshold valuemay be a 25% change or greater in a given process parameter. In anembodiment, each process parameter may have a different predeterminedthreshold value. For example, the predetermined threshold value for thepercentage change in the flow rate of a processing gas may be largerthan the predetermined threshold value for the percentage change in thetemperature of the substrate. In an additional embodiment, thepredetermined threshold value may be a maximum or minimum value for agiven processing parameter. For example, the predetermined thresholdvalue for the substrate temperature may be a maximum temperature. In yetanother embodiment, the type of predetermined threshold value may bedependent on the process parameter. For example, one or more processparameters in a processing recipe may have a predetermined thresholdvalue that is given as a maximum percentage change of the processparameter and other process parameters in the processing recipe may havea predetermined threshold value that is given as a maximum and/orminimum value.

Referring now to FIG. 6, a block diagram of an exemplary computer system660 of a processing tool is illustrated in accordance with anembodiment. In an embodiment, computer system 660 is coupled to andcontrols processing in the processing tool. Computer system 660 may beconnected (e.g., networked) to other machines in a Local Area Network(LAN), an intranet, an extranet, or the Internet. Computer system 660may operate in the capacity of a server or a client machine in aclient-server network environment, or as a peer machine in apeer-to-peer (or distributed) network environment. Computer system 660may be a personal computer (PC), a tablet PC, a set-top box (STB), aPersonal Digital Assistant (PDA), a cellular telephone, a web appliance,a server, a network router, switch or bridge, or any machine capable ofexecuting a set of instructions (sequential or otherwise) that specifyactions to be taken by that machine. Further, while only a singlemachine is illustrated for computer system 660, the term “machine” shallalso be taken to include any collection of machines (e.g., computers)that individually or jointly execute a set (or multiple sets) ofinstructions to perform any one or more of the methodologies describedherein.

Computer system 660 may include a computer program product, or software622, having a non-transitory machine-readable medium having storedthereon instructions, which may be used to program computer system 660(or other electronic devices) to perform a process according toembodiments. A machine-readable medium includes any mechanism forstoring or transmitting information in a form readable by a machine(e.g., a computer). For example, a machine-readable (e.g.,computer-readable) medium includes a machine (e.g., a computer) readablestorage medium (e.g., read only memory (“ROM”), random access memory(“RAM”), magnetic disk storage media, optical storage media, flashmemory devices, etc.), a machine (e.g., computer) readable transmissionmedium (electrical, optical, acoustical or other form of propagatedsignals (e.g., infrared signals, digital signals, etc.)), etc.

In an embodiment, computer system 660 includes a system processor 602, amain memory 604 (e.g., read-only memory (ROM), flash memory, dynamicrandom access memory (DRAM) such as synchronous DRAM (SDRAM) or RambusDRAM (RDRAM), etc.), a static memory 606 (e.g., flash memory, staticrandom access memory (SRAM), etc.), and a secondary memory 618 (e.g., adata storage device), which communicate with each other via a bus 630.

System processor 602 represents one or more general-purpose processingdevices such as a microsystem processor, central processing unit, or thelike. More particularly, the system processor may be a complexinstruction set computing (CISC) microsystem processor, reducedinstruction set computing (RISC) microsystem processor, very longinstruction word (VLIW) microsystem processor, a system processorimplementing other instruction sets, or system processors implementing acombination of instruction sets. System processor 602 may also be one ormore special-purpose processing devices such as an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), adigital signal system processor (DSP), network system processor, or thelike. System processor 602 is configured to execute the processing logic626 for performing the operations described herein.

The computer system 660 may further include a system network interfacedevice 608 for communicating with other devices or machines. Thecomputer system 660 may also include a video display unit 610 (e.g., aliquid crystal display (LCD), a light emitting diode display (LED), or acathode ray tube (CRT)), an alphanumeric input device 612 (e.g., akeyboard), a cursor control device 614 (e.g., a mouse), and a signalgeneration device 616 (e.g., a speaker).

The secondary memory 618 may include a machine-accessible storage medium631 (or more specifically a computer-readable storage medium) on whichis stored one or more sets of instructions (e.g., software 622)embodying any one or more of the methodologies or functions describedherein. The software 622 may also reside, completely or at leastpartially, within the main memory 604 and/or within the system processor602 during execution thereof by the computer system 660, the main memory604 and the system processor 602 also constituting machine-readablestorage media. The software 622 may further be transmitted or receivedover a network 620 via the system network interface device 608.

While the machine-accessible storage medium 631 is shown in an exemplaryembodiment to be a single medium, the term “machine-readable storagemedium” should be taken to include a single medium or multiple media(e.g., a centralized or distributed database, and/or associated cachesand servers) that store the one or more sets of instructions. The term“machine-readable storage medium” shall also be taken to include anymedium that is capable of storing or encoding a set of instructions forexecution by the machine and that cause the machine to perform any oneor more of the methodologies. The term “machine-readable storage medium”shall accordingly be taken to include, but not be limited to,solid-state memories, and optical and magnetic media.

In the foregoing specification, specific exemplary embodiments have beendescribed. It will be evident that various modifications may be madethereto without departing from the scope of the following claims. Thespecification and drawings are, accordingly, to be regarded in anillustrative sense rather than a restrictive sense.

What is claimed is:
 1. A real time etch rate sensor, comprising: a resonant system, comprising: a resonating body; a first electrode formed on a first surface of the resonating body; a second electrode formed over a second surface of the resonating body; and a sacrificial layer formed on the first electrode, wherein at least a portion of the first electrode is not covered by the sacrificial layer; and a conductive housing for securing the resonant system, wherein the conductive housing contacts the first electrode, and wherein at least a portion of an interior edge of the conductive housing is spaced away from the sacrificial layer.
 2. The real time etch rate sensor of claim 1, wherein the sacrificial layer is a material that may be selectively etched with respect to the first electrode in a radical only etching process.
 3. The real time etch rate sensor of claim 2, wherein the sacrificial layer is a dielectric material, a semiconductor material, or a conductive material.
 4. The real time etch rate sensor of claim 1, wherein the sacrificial layer does not contact the conductive housing.
 5. The real time etch rate sensor of claim 4, wherein the interior edge of the conductive housing is spaced away from the sacrificial layer by a gap that is approximately 5 mm or less.
 6. The real time etch rate sensor of claim 4, wherein the first electrode has a radius, and wherein the interior edge of the conductive housing is spaced away from the sacrificial layer by a gap that is approximately 5% of the radius of the first electrode or less.
 7. The real time etch rate sensor of claim 1, further comprising a plurality of additional sacrificial layers, wherein each of the plurality of additional sacrificial layers may be etched selective to each other, to the sacrificial layer and to the first electrode.
 8. The real time etch rate sensor of claim 7, wherein the sacrificial layer is formed over an approximate center of the first electrode, and wherein the additional sacrificial layers are formed in substantially concentric rings around the sacrificial layer.
 9. The real time etch rate sensor of claim 7, wherein each of the plurality of sacrificial layers is formed over a different region of the first electrode.
 10. The real time etch rate sensor of claim 1, wherein the resonating body is quartz, sapphire, silicon, germanium, or lead zirconate titanate.
 11. The real time etch rate sensor of claim 1, further comprising: a frequency bridge electrically coupled between the first electrode and the second electrode.
 12. The real time etch rate monitor of claim 11, wherein the first electrode is electrically coupled to a ground potential.
 13. A radical only etching process tool, comprising: a remote plasma chamber; a main processing chamber coupled to the remote plasma chamber, wherein the main processing chamber comprises: an upper portion; a lower portion, wherein the upper portion is separated from the lower portion by an ion filter; and a pump liner formed around a pedestal in the lower portion; and a real time etch rate sensor located in the lower portion of the main processing chamber, wherein the real time etch rate sensor comprises: a resonant system, comprising: a resonating body; a first electrode formed on a first surface of the resonating body; a second electrode formed over a second surface of the resonating body; and a sacrificial layer formed on the first electrode, wherein at least a portion of the first electrode is not covered by the sacrificial layer; and a conductive housing for securing the resonant system, wherein the conductive housing contacts the first electrode, and wherein at least a portion of an interior edge of the conductive housing is spaced away from the sacrificial layer.
 14. The radical only etching process tool of claim 13, wherein the real time etch rate sensor is coupled to a monitor outside of the main processing chamber by a probe that passes through a port in the lower portion of the main processing chamber.
 15. The radical only etching process tool of claim 14, wherein the pump liner is positioned between the pedestal and the real time etch rate sensor.
 16. The radical only etching process tool of claim 14, wherein the probe passes through an opening in the pump liner, and wherein the real time etch rate sensor is seated in the opening through the pump liner.
 17. The radical only etching process tool of claim 14, further comprising: an antechamber separated from the lower portion of the main chamber by a gate valve, wherein the probe is retractable through the valve so that the real time etch rate sensor is moveable between the antechamber and the lower portion of the main chamber.
 18. A method for etching a substrate with a closed loop process recipe, comprising: executing the process recipe on a substrate in a processing chamber, wherein the process recipe includes one or more process parameters and an endpoint criterion that is determinable from outputs obtained from a real time etch rate sensor located in the processing chamber, wherein the real time etch rate sensor comprises a first electrode formed on a first surface of the resonating body and a sacrificial layer formed on the first electrode; determining whether the endpoint criterion is satisfied by analyzing one or more outputs from the real time etch rate sensor; and terminating the process recipe once the endpoint criterion is satisfied.
 19. The method of claim 18, wherein the endpoint criterion is a total thickness of material removed, and wherein the one or more outputs from the real time etch rate sensor that are used to determine if the endpoint criterion is satisfied include a resonance frequency of the real time etch rate sensor prior to executing the process recipe and a present resonance frequency of the real time etch rate sensor after the process recipe has been initiated.
 20. The method of claim 19, wherein the closed loop process recipe is implemented with a plurality of processing chambers in order to provide chamber matching between the plurality of processing chambers. 